reframing the Empty IA5 string discussion

["Kurt D. Zeilenga" <Kurt@OpenLDAP.org>]

I see that there are few reasonable options here:
1) IA5 strings precludes zero-length values
2) IA5 strings allows zero-length values
   2A) a zero-length values only matches a zero-length value
   2B) a zero-length value matches " " (and all values
       equivalent to " ").

I prefer 1 over 2A over 2B (see prior posts for why).

(Regardless of the choice LDAPprep can and should be designed
to be idempotent.)